The present invention relates to a process for the preparation of a hydrogen-rich gas by transforming a carbon monoxide-containing gas with steam according to the water-gas shift reaction: EQU CO+H.sub.2 O.fwdarw.CO.sub.2 +H.sub.2
this conversion, which constitutes an important part in most of the industrial processes for the preparation of hydrogen, is generally effected in two steps in the presence of a catalyst. The first conversion step, which is performed at a temperature of over 300.degree. C., is known as water-gas shift reaction at elevated temperature. In the second conversion step, the water-gas shift reaction at low temperature, a temperature below 300.degree. C. is used. As most of the catalysts proposed previously for the water-gas shift reaction are only sufficiently active in a fairly limited temperature range, it is customary to use different catalysts in each of the two conversion steps.
A major drawback of most of the catalysts proposed for the water-gas shift reaction is their sensitivity to the presence of sulphur in the gas to be transformed. This applies particularly to catalysts proposed for the water-gas shift reaction at low temperature, these catalysts being poisoned in a very short period of time by the presence of sulphur in the gas. Although this drawback exists to a lesser degree with the catalysts proposed for the water-gas shift reaction at elevated temperature, nonetheless a certain number of these catalysts diminish activity considerably in the presence of sulphur in the gas to be transformed, especially where the sulphur concentration is fairly high.
The carbon monoxide-containing gas which has to be transformed in most of the industrial processes for the preparation of hydrogen by the water-gas shift reaction is generally obtained by the incomplete combustion of sulphur- and/or carbon-containing hydrocarbon oil and it therefore contains sulphur. Because of the sensitivity to sulphur of the catalyst used in the water-gas shift reaction, the sulphur must therefore be carefully eliminated from the gas mixture before the latter is subjected to the water-gas shift reaction. This sulphur elimination is generally effected in a separate operational step and it is effected at low temperature.
The necessity of effecting a desulphurization step at low temperature in the preparation of hydrogen prior to the water-gas shift reaction is extremely disadvantageous from the point of view of heat consumption. In this case the sulphur-containing gas, which is at a relatively elevated temperature, must in fact first be cooled and subsequently reheated, after the desulphurization, to the temperature required for the water-gas shift reaction at elevated temperature. As a result, there has existed an urgent need for catalysts for the water-gas shift reaction which are not modified by the presence of sulphur in the gas to be transformed, so that the sulphur-containing gases may be subjected to the reaction without prior sulphur elimination.